1. Field of the Invention
The present invention relates to a stationary induction apparatus such as a transformer and a reactor.
2. Description of the Prior Art
FIG. 9 is a cross sectional view showing an example of a conventional core type oil-supplied transformer disclosed, for example, in the Patent Application Disclosure No.78109-1981. In FIG. 9, numeral 1 denotes a tank of a main unit, 2 is a core, 3 is an internal coil group inserted into a leg part of the core 2, 4 is an external coil group arranged on an external periphery of the internal coil group 3, 5 is a core clamp fixture which clamps a yoke part of the core 2 and simultaneously supports the internal coil group 3 and the external coil group 4. The core 2 is formed by stacking up silicon steel sheets in multiple layers with a clearance 2a provided therebetween adjacent layers of silicon steel sheets and constructed so as to permit a refrigerant to pass through these clearances 2a. The internal coil group 3 is formed by stacking up disc type coils 3a, wherein a spacer 3a1 is inserted respectively between every two adjacent coils so that the refrigerant passes through the disc type coils and spacers. The external coil group 4 is formed by stacking up disc type coils 4a, wherein a spacer 4a1 is inserted respectively between every two adjacent coils. 6 is an insulation plate inserted between the internal coil group 3 and the external coil group 4 and the core clamp fixture 5, and a plurality of refrigerant flow ports 6a through which the refrigerant is permitted to flow are provided at respective intermediate positions of the insulation plate 6 and the core clamp fixture 5, with which the internal coil group 3 and the external coil group 4 come in contact, at equal pitches of distance in the circumferential direction. 7 is an insulation barrier provided between the internal coil group 3 and the external coil group 4 and 8 is an insulation barrier between the external coil group 4 and the tank 1. 9 is a cooler which discharges a loss heat such as a Joule heat which is produced in the main unit due to the circulation of the refrigerant, 10 is a pump which circulates the refrigerant, 11 is a piping which connects the upper part of the tank 1 and the upper part of the cooler 9, and 12 is a piping which connects the lower part of the cooler 9 and the lower part of the tank 1. 13 is a side pipe for limiting the flow of refrigerant in the internal coil group 3 and the external coil group 4 included in the main unit to a fixed volume and 14 is a control valve for controlling the volume of refrigerant which flows in the side pipe 13. 15 is a refrigerant chamber which discharges the refrigerant cooled in the cooler 9.
The tank 1 of the main unit is filled with an insulation oil which serves as a refrigerant.
FIG.10 shows an embodiment as a shell type oil-supplied transformer is viewed from a position where the coil is seen in the horizontal direction. In FIG. 10, 21 is a main unit tank, 22 is a core, 23 is a low voltage coil group formed by stacking up a plurality of low voltage coils 23a which are arranged to traverse the core 22, 24 is a high voltage coil group formed by stacking up a plurality of high voltage coils 24a which are arranged to traverse the core 22. The low voltage coil group 23 and the high voltage coil group 24 are respectively formed by stacking up low voltage coils 23a and high voltage coils 24a, which are respectively wound in the shape of flat plate, in multiple layers, and the high voltage coil group 24 is arranged at the center and the low voltage coil group 23 is divided into two groups, which are respectively arranged both above and below the high voltage coil group 24. Spacers, not shown, are inserted between plate type low voltage coils 23a and high voltage coils 24a which are arranged in multiple layers to maintain spaces through which the refrigerant flows. 25 is refrigerant flow guides which are arranged so as to surround the coil groups expect for the opposing sides of the low voltage coil group 23 and the high voltage coil group 24, so that one of the sides forms an refrigerant inlet port and another one forms a refrigerant outlet port. 26 is an insuIation plate which secures a refrigerant passage inside the low voltage coil group 23 and the high voltage coil group 24 by arranging the refrigerant passage along the upper and lower surfaces on which the two divided low voltage coil group 23 and the high voltage coil group 24 are stacked up in multiple layers and also ensures a dielectric strength between the low voltage and high voltage coil groups 23 and 24 and the core 22. 29 is a cooler, 30 is a pump, and 31 and 32 are a piping which connects the cooler 29 and the tank 21. 35a and 35b denote refrigerant chamber through which the refrigerant flows into the tank and through which the refrigerant flows out from the tank, respectively.
The operation of the stationary induction apparatus is described below. In a core type oil-supplied transformer shown in FIG. 9, a refrigerant contained in a tank 1 is pressurized by a pump 10 to flow into a lower part of the tank 1, then flows to the sides of an internal coil group 3 and an external coil group 4 through a refrigerant flow port 6a provided in a core clamp fixture 5 and an insulation plate 6 and is divided into a flow passage which flows up along the sides of the internal coil group 3 and the external coil group 4 to reach the upper part of the tank and a flow passage which flows up through an intermediate clearance 2a of the core 2 and a space between the core 2 and the internal coil group 3 to reach the upper part of the tank, then flows up into the upper part of the tank 1 while cooling the internal coil group 3, the external coil group 4 and the core 2. Since there is a problem that, if the flow rate of the refrigerant which passes through the internal coil group 3 and the external coil group 4 is excessively accelerated, a static charge is produced due to friction between the refrigerant and the insulation material applied to the surfaces of the coils and accumulated on the surface of this insulation material and, if the accumulated static charge exceeds the limit, static discharging may occur to trigger a dielectric breakdown, the discharge from the pump 1O is shunted to a side piping 13 so that the flow rate of refrigerant at the sides of the internal coil group 3 and the external coil group 4 does not exceed the specified value and the refrigerant flow is by-passed by a control valve 14 to the upper part of the tank 1 to control the flow rate, thus controlling the flow rate of refrigerant along the sides of the internal coil group 3 and the external coil group 4. The refrigerant in the upper part of the tank 1 is sucked by the cooler 9 through the piping 11 and goes down to reach the pump 10 while being cooled, thus this refrigerant is circulated through this channel.
In a shell type oil-supplied transformer shown in FIG. 10, a low voltage coil group 23 and a high voltage coil group 24 are arranged in multiple layers and a refrigerant in a tank 21 is pressurized by a pump 30 to flow into a refrigerant chamber 35a located at the left side in the tank 21 as shown, then shunted into a channel from a refrigerant flow inlet 25a provided in the coil groups 23 and 24 to reach a refrigerant flow outlet 25b through tiered clearances of the low voltage coil group 23 and the high voltage coil group 24 and flow to a refrigerant chamber 35b at the right side in the tank 21 as shown while cooling the low voltage coil group 23 and the high voltage coil group 24 and a channel where the refrigerant flows up along the multiple-layered surfaces of the core 22, then flows into the refrigerant chamber 35b at the right side in the tank 21 as shown. The refrigerant in the refrigerant chamber 35b at the right side in the tank 21 as shown is sucked and cooled by the cooler 29 and circulated through a channel which reaches the pump 30. Though not shown, a refrigerant passage is formed between the core 22 and the tank 21 and between the core 22 and the low voltage coil group 23 and the high voltage coil group 24 so as to optimize cooling of the core 22.
[Subjects to be Solved by the Invention]
The conventional stationary induction apparatus with the construction as described above includes the problems as described below.
In the core type oil-supplied transformer shown in FIG. 9, there is a problem that the refrigerant which has passed the part including the internal coil group 3, external coil group 4 and core 2 is mixed with the refrigerant which has been by-passed through the side piping 13 without passing through the main unit to lower its temperature and flows into the cooler 9 while its temperature is kept low, and it is necessary to increase the number of coolers to ensure the specified radiation value in the cooler 9 and, on the other hand, there is a problem that a static charge occurs, as described above, if the flow rate of refrigerant which flows through the part including the internal coil group 3 and the external coil group 4 is accelerated and therefore the flow rate cannot be increased over the specified value. Accordingly, there is further a problem that it is necessary to take a measure for reducing the density of the current to reduce heat loss which occurs in the internal coil group 3 and the external coil group 4 and therefore the dimensions of the apparatus will be larger.
In a shell type oil-supplied transformer shown in FIG. 10, the refrigerant flows into the low voltage coil group 23 and the high voltage coil group 24 through the refrigerant flow inlet port 25a provided at one ends of the low voltage coil group 23 and the high voltage coil group 24, flows through the flow passage shown with W in FIG. 10 and flows out from the refrigerant flow outlet port 25b provided at the other ends of the above coil groups. Accordingly, the area of the flow passage is small and the length of the flow passage is long and therefore the temperature of refrigerant between the refrigerant flow inlet port 25a and the refrigerant flow outlet port 25b rises and it is necessary to increase the flow rate of the refrigerant by accelerating the flow speed. However, if the flow speed is accelerated, the above described problem of static charge is anticipated and therefore there is a problem that a measure is required to control the quantity of heat to be produced to a low level by designing the density of the current which flows through the coils of the low voltage coil group 23 and the high voltage coil group 24 and the apparatus requires larger dimensions.
In the above description, it is assumed that an insulation oil is used as the refrigerant; however, the transformer can be a gas-supplied type transformer by using an insulation gas such as SF6 gas as the refrigerant.
In this case, the thermal capacity per volume of SF6 gas used as the refrigerant is smaller than that of the insulation oil and therefore the flow rate of the refrigerant need be larger. However, it is limited to increase the flow rate of gas in the coil groups in the same construction as the oil-supplied type transformer and therefore there is a problem that a measure is required, for example, to reduce the density of a current which flows in the coils as in the case of the insulation oil so that a heat loss which occurs in the coil groups may be small and the dimensions of the apparatus become larger.